Crystal Growth of Aluminum Magnesium Borides from Al-Mg-B Ternary System Solutions and Properties of the Crystals

Single crystals of AlMgB 14 and AlMgB 22 were grown from a high-temperature aluminum metal flux in an Ar atmosphere. The optimum conditions for growing AlMgB 22 and AlMgB 14 were established using the starting mixtures of B/Mg=0.5-1.0 and B/Mg=2.0-6.0. The AlMgB 14 and AlMgB 22 crystals obtained have well-developed {001} and {100} faces, and were black with a metallic luster. The maximum dimensions of these crystals were about 5.2 mm and 4.6 mm, respectively. The values of micro-Vickers hardness of the AlMgB 14 and AlMgB 22 crystals are in the ranges of 23.9±0.6-27.6±0.6 GPa. The oxidation process of AlMgB 14 and AlMgB 22 crystals were studied up to 1473 K by TG-DTA method. The susceptibility of AlMgB14 with an increase at low temperatures does not show any particular features, being indicative of a paramagnetic contribution, which is likely due to impurities. The susceptibility of the AlMgB 22 sample shows no apparent contribution from impurities and also does not have any anomalous behavior.